The present invention relates to a method and device for deploying a restraint system in response to the impact of a motor vehicle against an obstacle. An acceleration sensor arrangement is included that has two sensitivity axes oriented in different directions, and an evaluation circuit generating a trigger signal for the restraint system from measured accelerations.
U.S. Pat. No. 5,202,831 describes that two acceleration sensors are provided for detecting front-end, rear-end, and lateral impacts. One of the two acceleration sensors has a sensitivity axis in the longitudinal direction of the motor vehicle and the other has a sensitivity axis in the transverse direction of the motor vehicle. Using a device of this type, it is possible to distinguish between a front-end or a rear-end impact and a lateral impact, so that the corresponding front-end or lateral airbags can be deployed.
One important goal in the design of restraint systems in a motor vehicle is to prevent a false deployment of airbags, i.e., depending on the direction of impact, only those airbags should be deployed that offer the vehicle passengers actual protection. To guard against a false deployment of restraint devices, it is conventional, as described in German Patent 195 14 082 to make the deployment depend not only on the response signal of an acceleration sensor, but rather to design the acceleration sensor arrangement in a redundant manner. Often, in addition to acceleration sensors, safety switches (safing or arming sensors) are used. As a result of the redundant design, the expense of the restraint system is increased in an undesirable manner.
An acceleration sensor system that is designed in a redundant manner is also known from European Patent 0 785 112 A1. In this context, two or three acceleration sensors are arranged in the rotor vehicle in different locations. The acceleration sensors are arranged so that their sensitivity axes are oriented parallel to each other. The sensitivity axes therefore all point in the same direction, so that all acceleration sensors react to an acceleration of the vehicle occuring in the direction of the common sensitivity axes. Finally, the reaction of one acceleration sensor is rendered plausible by the reaction of one or two other redundant acceleration sensors.
An acceleration sensor system that is designed in a redundant manner is described in European Patent No. 0785 112. In this sensor system, two or three acceleration sensors are arranged in the motor vehicle at different locations. The acceleration sensors are arranged such that their sensitivity axes are oriented parallel to each other. Therefore, the sensitivity axes all point in the same direction, so that all acceleration sensors react to an acceleration of the vehicle occurring in the direction of the common sensitivity axes. Finally, the reaction of one acceleration sensor is rendered plausible by the reaction of one or two other redundant acceleration sensors.
An object of the present invention is to provide a method and a device that provide high reliability with respect to false deployments of the restraint system at the least possible expense for the acceleration sensor arrangement.
The object is achieved by using an acceleration sensor arrangement that has two sensitivity axes oriented in different directions and by using the acceleration measured with respect to one of the two sensitivity axes in the plausibility check of a deployment decision. An evaluation circuit determines the deployment decision from the acceleration measured with respect to the other sensitivity axis. A trigger signal is only emitted when a deployment decision signal and a plausibility signal are present at the inputs of an AND logic circuit at the same time. The expense of the device according to the present invention is reduced in comparison to conventional devices because, using the acceleration sensors necessary for measuring the accelerations of the vehicle in the longitudinal and transverse directions, a reciprocal plausibility check is carried out, and therefore redundant acceleration sensors are not required.
Thus, given two acceleration sensor elements that have different sensitivity axes, a reciprocal plausibility check can be carried out.
It is possible to use three acceleration sensor elements, of which two have sensitivity axes oriented in the same direction and the third acceleration sensor element has a sensitivity axis oriented in a different direction. In this context, one of the two acceleration sensor elements that has sensitivity axes oriented in the same direction is brought to bear on the plausibility check of the third acceleration sensor element.
In order to be able to distinguish front-end or rear-end impacts and lateral impacts clearly from each other, it is advantageous that one sensitivity axis be oriented in the longitudinal direction and the other sensitivity axis be oriented in the transverse direction of the motor vehicle.
An acceleration sensor element arranged centrally in the motor vehicle that has a sensitivity axis in the transverse direction of the motor vehicle can be brought to bear, for the plausibility check, by one or a plurality of lateral impact sensors arranged on the periphery.
The plausibility check can be carried out as a threshold decision with respect to the amplitude, the gradient or the polarity of the measured acceleration or the integral of the measured acceleration.